qline/qline.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strings"

	"tildegit.org/sloum/qline/termios"
)

const (
	UpArrow rune = iota - 20
	DownArrow
	LeftArrow
	RightArrow
	Delete
	Home
	End
	PrintScreen
	PageUp
	PageDown
	Escape rune = 27
	NewLine rune = 10
	CarriageReturn rune = 13
	BackSpace rune = 127
)

var (
	width int
)

type Buffer struct {
	buf []rune
	cursor int
	maxWidth int
	offset int
	cursorStart int
	prompt string
}

func (lb Buffer) String() string {
	return string(lb.buf)
}

func (lb *Buffer) deleteChar() {
	if lb.cursor == len(lb.buf) {
		return
	} else if lb.cursor == len(lb.buf)-1 {
		lb.buf = lb.buf[:len(lb.buf)-1]
	} else {
		lb.buf = append(lb.buf[:lb.cursor], lb.buf[lb.cursor+1:]...)
	}
	if lb.offset > 0 {
		lb.offset--
	}
}

// TODO rework this so that the changes are made but all drawing to the screen comes
// from one source and always draws the whole input area. This will make dealing with
// offsets much easier.
func (lb *Buffer) addChar(c rune, echo bool) {
	if c < 9 || (c > 10 && c < 13) || (c > 13 && c < 32) {
		return
	}
	if lb.cursor == len(lb.buf) {
		lb.buf = append(lb.buf, c)
		lb.cursor++
	} else {
		lb.buf = append(lb.buf[:lb.cursor+1], lb.buf[lb.cursor:]...)
		lb.buf[lb.cursor] = c
		lb.cursor++
	}
	if lb.cursor - lb.offset > lb.maxWidth {
		lb.offset++
	}
	if echo {
		lb.printBuf()
	}
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func (lb Buffer) printBuf() {
	out := lb.buf[lb.offset:min(len(lb.buf), lb.offset+lb.maxWidth)]
	fmt.Printf("\r%s%s\033[0K\r\033[%dC", lb.prompt, string(out), lb.cursor - lb.offset + len(lb.prompt))
}

func (lb *Buffer) controlInput(c rune) {
	switch c {
	case Delete:
		lb.deleteChar()
	case BackSpace:
		if lb.cursor > 0 {
			lb.cursor--
			lb.deleteChar()
		}
	case LeftArrow:
		if lb.offset > 0 && lb.cursor - lb.offset == 0 {
			lb.offset--
		}
		if lb.cursor > 0 {
			lb.cursor--
		}
	case RightArrow:
		// FIXME: This still isnt working quite right...
		for ;lb.cursor - lb.offset >= lb.maxWidth && lb.cursor < len(lb.buf); {
			lb.offset++
		}
		if lb.cursor < len(lb.buf) {
			lb.cursor++
		}
	case Home:
			lb.offset = 0
			lb.cursor = 0
	case End:
		if lb.cursor < len(lb.buf) {
			lb.cursor = len(lb.buf)
			lb.offset = max(lb.cursor - lb.maxWidth, 0)
		}
	}
	lb.printBuf()
}

func (lb *Buffer) seedContent(s string) {
	for _, r := range s {
		lb.addChar(r, false)
	}
}

func parseCursorPosition(esc string) (int, int, error) {
	var row, col int
	r := strings.NewReader(esc)
	_, err := fmt.Fscanf(r, "\033[%d;%dR", &row, &col)
	return row, col, err
}

func GetText(prompt string, content string) string {
	cols, _ := termios.GetWindowSize()
	b := Buffer{make([]rune, 0, (len(content)+1)*2), 0, cols-len(prompt), 0, 0, prompt}
	b.seedContent(content)

	fmt.Print(prompt)
	fmt.Print("\033[6n")
	b.printBuf()

	var ch rune
	var err error
	reader := bufio.NewReader(os.Stdin)

	for {
		ch, err = readKey(reader)
		if err != nil && err.Error() == "response" {
			b.cursorStart = int(ch)
			b.maxWidth = cols - b.cursorStart
		} else if err != nil {
			continue
		}
		if ch == CarriageReturn || ch == NewLine {
			break
		}

		if isControl(ch) {
			b.controlInput(ch)
		} else {
			b.addChar(ch, true)
		}

	}
	return b.String()
}


func readKey(reader *bufio.Reader) (rune, error) {
	char, _, err := reader.ReadRune()
	if err != nil {
		return 0, err
	}
	avail := reader.Buffered()
	if char == Escape && avail > 0 {
		var b strings.Builder
		b.WriteRune(27)
		for ; avail > 0; avail-- {
			c, _, e := reader.ReadRune()
			if e != nil {
				break
			}
			b.WriteRune(c)
		}
		escSeq := b.String()
		switch true {
		case escSeq == "\033[A":
			char = UpArrow
		case escSeq == "\033[B":
			char = DownArrow
		case escSeq == "\033[C":
			char = RightArrow
		case escSeq == "\033[D":
			char = LeftArrow
		case escSeq == "\033[5~":
			char = PageUp
		case escSeq == "\033[6~":
			char = PageDown
		case isHomeKey(escSeq):
			char = Home
		case isEndKey(escSeq):
			char = End
		case isDeleteKey(escSeq):
			char = Delete
		case escSeq[len(escSeq)-1] == 'R':
			_, cols, err := parseCursorPosition(escSeq)
			if err == nil {
				err = fmt.Errorf("response")
			}
			return rune(cols), err
		default:
			fmt.Printf("Odd sequence: %s\n", escSeq[1:])
		}
	}
	return char, nil
}

func isControl(c rune) bool {
	switch c {
		case UpArrow, DownArrow, RightArrow, LeftArrow, PageUp, PageDown, Home, End, Delete, BackSpace, CarriageReturn, NewLine, Escape:
			return true
		default:
			return false
	}
}

func isDeleteKey(seq string) bool {
	switch seq {
	case "\033[3~", "\033[P":
		return true
	default:
		return false
	}
}

func isHomeKey(seq string) bool {
	switch seq {
	case "\033[1~", "\033[7~", "\033[H", "\033OH":
		return true
	default:
		return false
	}
}

func isEndKey(seq string) bool {
	switch seq {
	case "\033[4~", "\033[8~", "\033[F", "\033OF":
		return true
	default:
		return false
	}
}

func PrintKey(k rune) {
	switch true {
	case k == UpArrow:
		fmt.Println("UpArrow")
	case k == DownArrow:
		fmt.Println("DownArrow")
	case k == LeftArrow:
		fmt.Println("LeftArrow")
	case k == RightArrow:
		fmt.Println("RightArrow")
	case k == Escape:
		fmt.Println("Escape")
	case k == NewLine:
		fmt.Println("NewLine")
	case k == CarriageReturn:
		fmt.Println("CarriageReturn")
	case k == Delete:
		fmt.Println("Delete")
	case k == Home:
		fmt.Println("Home")
	case k == End:
		fmt.Println("End")
	case k == BackSpace:
		fmt.Println("BackSpace")
	default:
		fmt.Printf("%c (%d)\n", k, k)
	}

}

func main() {
	// This main func is just for testing and will
	// be removed with the intention that this just
	// gets used as a lib
	termios.SetCharMode()
	defer termios.Restore()
	str := ""

	for {
		fmt.Print("\n")
		str = GetText("> ", str)
	}
}